Modern vehicles use wireless key fobs that restrict both interior access as well as the ability to operate the vehicle. Authorized vehicle users can carry a wireless key fob and as they approach the vehicle, the PEPS system can determine whether the unique wireless signal transmitted by the key fob is authorized for access and/or operation of the vehicle. If so, the vehicle user can enter and subsequently start the vehicle. More specifically, the PEPS system defines a plurality of virtual zones surrounding the vehicle and monitors these zones for the presence of the key fob. Each of the zones is generally associated with a different level of vehicle access and functionality. In some cases, the presence of the key fob being detected in a particular zone may automatically initiate one or more vehicle functions.
When initially introduced, PEPS systems and key fobs communicated using wireless signals that fall on the low end of the frequency spectrum (e.g., ˜30-400 kHz). However, with the continued advancement of technology, vehicles are more frequently becoming equipped with an ability to facilitate communication with other wireless devices using short-range wireless signals through various wireless protocols, such as Bluetooth Low-Energy (LE) or Wi-Fi. Consequently, PEPS systems previously dedicated to low-frequency signal transmission are being replaced with PEPS systems configured to communicate using the Bluetooth LE and/or Wi-Fi communication technologies. With these advanced wireless communications capabilities, the PEPS systems are also being configured to use mobile wireless devices to control vehicle access and functionality in lieu of, or in addition to, key fobs.
When using a mobile wireless device for passive vehicle entry, the PEPS system determines the location of the mobile device using data obtained from the wireless signals communicated between the vehicle and the mobile device. In one implementation, the location of the mobile device is determined using performance variables associated with the wireless signals, such as signal strength and/or signal direction. For example, determining the location may include a calculation that compares a plurality of known distance-to-signal strength values stored at the vehicle to performance variables measured at various nodes of the vehicle. That is, signal strength values for each amount of distance from the vehicle can be stored and referred to when calculating the location of the mobile device. However, radio frequency (RF) performance characteristics (e.g., transmit power, receiver sensitivity, and antenna gain) vary by design from one mobile device to another, which may impact the performance and accuracy of the PEPS system in determining the location of the mobile device. In other words, when there are variances in the mobile device RF performance characteristics relative to the stored performance variables used to determine location, the PEPS system may inaccurately identify the location of the mobile device, and thus, the presence of the mobile device within a particular zone. As a result, the mobile device may be unable to obtain vehicle access and/or functionality that would otherwise be associated with its location.
To provide consistency in its performance and accuracy, it may be desirable to calibrate a vehicle PEPS system with respect to the RF performance characteristics associated with each individual mobile wireless device used by authorized users of the same vehicle.